Miscibility gap between jadeite and omphacite

Abstract

Coexisting jadeite and omphacite were found in a jadetite from the Ohmi area and in a jadeite vein from the Shibukawa area, central Japan. EPMA scanning traverses confirm the existence of miscibility gaps between jadeite and omphacite. The gaps are impure jadeite (Jd>86)–omphacite (Jd<65) in the Ohmi sample and jadeite (Jd>90)–impure jadeite (85>Jd>77) and impure jadeite (85>Jd>77)–omphacite (Jd<50) in the Shibukawa sample. It is concluded that the miscibility gap narrows with increasing grade, especially from the omphacite side, and two miscibility gaps, which were found in the Shibukawa sample, occur only under low-grade metamorphic conditions.